A blowout preventer (BOP) is a large, specialized valve or similar mechanical device that is used to seal, control and monitor oil and gas wells, including land wells, offshore rigs and subsea wells. BOPs are designed primarily to cope with extreme erratic pressures and uncontrolled flow (formation kick) emanating from a well reservoir during drilling to prevent blowouts (i.e. the uncontrolled release of oil and gas at high pressure from a wellbore) and to prevent tubing, tools and drilling fluid from being blown out of the wellbore. BOPs are required at every wellhead during drilling for safety reasons, and are the last line of defense in preventing blowouts.
Typically a BOP stack is used, which is an assembly of several stacked BOPs of varying function and type, and is also referred to as a stack or a BOP. There are two general types of BOPs: annular and ram. A typical BOP stack usually has at least one annular BOP stacked above several ram BOPs, along with auxiliary components such as electrical and hydraulic lines. On land rigs, a BOP stack may have a bore diameter of 13″ or greater and be rated for working pressure up to and exceeding 10,000 psi. A BOP stack may be tens of feet tall and weigh tens of thousands of pounds.
The size and weight of a BOP stack provides several challenges to lifting, lowering, and transporting a BOP stack to or from the wellhead. Installing a BOP stack on a wellhead is particularly challenging and is a time consuming operation requiring fine movements. First the stack must be positioned beneath the drill floor and directly over a wellhead, centered on the axis of the well, which typically requires fine adjustment of the BOP stack along a horizontal axis and possibly a vertical axis. Since the BOP stack generally connects to the wellhead by a flange, the BOP stack must be rotated about its vertical axis to align the bolt patterns on the BOP stack flange with the casing bowl bolt patterns at the wellhead.
BOP handling systems typically comprise an overhead lifting system, such as a crane or trolley, to lift a BOP off a skid and transport it to the wellhead. There are many safety risks with handling such a large, heavy piece of equipment, especially because there are generally people working on, near or under the BOP stack while it is being handled. Weather conditions, such as high wind velocities, can also increase the risks associated with handling BOP stacks.
BOP stacks are not generally manufactured to include a mechanism for handling the BOP, so typically an after-market clamp is attached to the BOP stack to provide attachment points for the handling system. Most handling systems are top-supporting systems that hoist the BOP stack from an overhead device.
BOP clamps are typically installed around the BOP stack under the top annular BOP. Most clamps are comprised of two pieces that are bolted together around the BOP stack, which allows the clamp to be secured to the BOP stack without removing the annular BOP. The use of bolts for securing the clamp together raises safety issues since most clamps are not installed by mechanics but by workers who may not understand and use proper bolt torque techniques and values. Additionally, bolts can go missing and improper grades of bolt materials can be used. This can create serious safety problems when used for handling a highly loaded overhead item like a BOP stack. Furthermore, BOP clamps often extend up the side of an annular BOP and interfere with hydraulic and electrical lines, resulting in the clamps and/or lines having to be modified in the field. Not only is this time-consuming, but it also creates safety risks if the clamps and/or hydraulic/electrical lines are used in an unintended manner.
U.S. Patent Publication No. 2014/0265389 provides a BOP lifting apparatus comprising a frame with a U-shaped central recess that fits around a BOP stack, and a pivotable gate attached to the frame that can be opened or closed around the BOP stack using an actuator.
U.S. Pat. No. 7,040,411 provides a BOP handling system comprising a cart/skid, a tilting frame and a lifting frame to allow for movement of a BOP stack from a horizontal position to a vertical position. This handling system does not allow for lifting the BOP stack in a vertical direction which is often needed for moving and changing around BOP stacks at a well.
U.S. Pat. No. 4,630,347 discloses a hydrant tool assembly for installing or removing a seat ring and valve from a hydrant shoe located beneath the hydrant. The tool assembly includes a two piece gripper clamp for locking the upper and lower barrels of the hydrant together. The clamp is not designed for lifting functions, nor for supporting a heavy load such as a BOP stack.
There is a need for a BOP handling system/clamp that is compact and can efficiently and effectively attach to a BOP stack without having to disassemble the BOP stack and without interfering with the structure of the BOP stack. There is a further need for a BOP handling system/clamp that can support the load of a BOP stack to lift the BOP stack.